A combustion section of a gas turbine generally includes a plurality of combustors that are arranged in an annular array around an outer casing such as a compressor discharge casing. Pressurized air flows from a compressor to the compressor discharge casing and is routed to each combustor. Fuel from a fuel nozzle is mixed with the pressurized air in each combustor to form a combustible mixture within a primary combustion zone of the combustor. The combustible mixture is burned to produce hot combustion gases having a high pressure and high velocity.
In a typical combustor, the combustion gases are routed towards an inlet of a turbine of the gas turbine through a hot gas path that is at least partially defined by an annular combustion liner and an annular transition duct that extends downstream from the combustion liner and terminates at the inlet to the turbine. Thermal and kinetic energy are transferred from the combustion gases to the turbine to cause the turbine to rotate, thereby producing mechanical work. For example, the turbine may be coupled to a shaft that drives a generator to produce electricity.
In particular combustors, a combustion module is utilized to inject a generally lean fuel-air mixture into the hot gas path downstream from the primary combustion zone. The combustion module generally includes an annular fuel distribution manifold that circumferentially surrounds a portion of a cap assembly that partially surrounds the fuel nozzle, and a fuel injection assembly that extends between the fuel distribution manifold and the inlet to the gas turbine. The fuel injection assembly includes an annular combustion liner that extends continuously between the cap assembly and the inlet to the turbine. The continuously extending combustion liner defines the hot gas path within the combustor, thereby eliminating the separate transition duct. The combustion liner includes an annular main body that comprises of a conical section having a substantially circular cross section and a transition section that extends downstream from the conical section and that has a substantially non-circular cross section. The fuel injection assembly further includes a plurality of radially extending fuel injectors, also known as late lean fuel injectors that inject the lean fuel-air combustible mixture into the hot gas path downstream from the primary combustion zone. As a result, the combustion gas temperature is increased and the thermodynamic efficiency of the combustor is improved without producing a corresponding increase in the production of undesirable emissions such as oxides of nitrogen (NOX). However, the increase in the temperature of the combustion gases results in an increase of thermal stresses on the combustion liner.
One technique for cooling the combustion liner of the combustion module includes surrounding the combustion liner with a flow sleeve assembly so as to define a cooling flow passage therebetween, and routing a portion of the compressed working fluid through the cooling passage to provide at least one of impingement, convective or conductive cooling to the combustion liner. The flow sleeve assembly generally includes an annular support sleeve that surrounds a forward end portion of the combustion liner and that is positioned concentrically within the fuel distribution manifold, an annular flow sleeve that is coupled to an aft end of the support sleeve and that surrounds the conical section of the combustion liner, and an annular impingement sleeve that is coupled to an aft end of the flow sleeve and that surrounds the transition section of the combustion liner.
While the flow sleeve assembly is generally effective for cooling the combustion liner, the multiple connections between the various components may leak or develop leaks over time due to tolerance issues and/or due to thermal and/or mechanical cycle fatigue, thereby impacting the overall cooling effectiveness and durability of the flow sleeve assembly. In addition, the loss of the compressed working fluid from the cooling passage may result in a decrease of combustor performance due to a decrease in the amount of the compressed working fluid that is routed to the fuel nozzle for combustion. Furthermore, the multiple components increase time and costs associated with assembly, disassembly and the manufacture of the combustion module. Therefore, an improved system for cooling the combustion liner of the combustion module would be useful.